In the medical field, where beneficial agents are collected, processed and stored in containers, transported and ultimately delivered through tubes by infusion to patients, there has been a recent trend toward developing materials useful for fabricating such containers and tubing without the disadvantages of currently used materials such as polyvinyl chloride. These new materials for tubings must have a unique combination of properties, so that the tubing may be used in fluid administration sets. Among these are the materials must be optically clear, environmentally compatible, have sufficient yield strength and flexibility, have a low quantity of low molecular weight additives, and be compatible with medical solutions.
It is desirable for medical tubing to be optically transparent to allow for visual inspection of fluids in the tubing.
It is also a requirement that the tubing materials be environmentally compatible as a great deal of medical tubing is disposed of in landfills and through incineration. Further benefits are realized by using a material which is thermoplastically recyclable so that scrap generated during manufacturing may be incorporated into virgin material and refabricated into other useful articles.
For tubing that is disposed of by incineration, it is necessary to use a material that does not generate or minimizes the formation of by-products such as inorganic acids which may be environmentally harmful, irritating, and corrosive. For example, PVC may generate objectionable amounts of hydrogen chloride (or hydrochloric acid when contacted with water) upon incineration, causing corrosion of the incinerator and possible pollution to the environment.
To be compatible with medical solutions, it is desirable that the tubing material be free from or have a minimal content of low molecular weight additives such as plasticizers, stabilizers and the like. These components could be extracted into the therapeutic solutions that come into contact with the material. The additives may react with the therapeutic agents or otherwise render the solution ineffective. This is especially troublesome in bio-tech drug formulations where the concentration of the drug is measured in parts per million (ppm), rather than in weight or volume percentages. Even minuscule losses of the bio-tech drug can render the formulation unusable. Because bio-tech formulations can cost several thousand dollars per dose, it is imperative that the dosage not be changed.
Polyvinyl chloride ("PVC") has been widely used to fabricate medical tubings as it meets most of these requirements. However, because PVC by itself is a rigid polymer, low molecular weight components known as plasticizers must be added to render PVC flexible. As set forth above, these plasticizers may leach out of the tubing and into the fluid passing through the tubing to contaminate the fluid or to render the fluid unusable. For this reason, and because of the difficulties encountered in incinerating PVC, there is a need to replace PVC medical tubing.
Polyolefins have been developed which meet many of the requirements of medical containers and tubing, without the disadvantages associated with PVC. Polyolefins typically are compatible with medical applications because they have minimal extractability to the fluids and contents which they contact. Most polyolefins are environmentally sound as they do not generate harmful degradants upon incineration, and in most cases are capable of being thermoplastically recycled. Many polyolefins are cost effective materials that may provide an economic alternative to PVC. However, there are many hurdles to overcome to replace all the favorable attributes of PVC with a polyolefin.
For example, because of the inert nature of polyolefins, due in part to the non-polar nature of the polymer, difficulties have been encountered in bonding the polyolefin materials to polar molecules, such as polycarbonates, ABS and acrylic polymers. Typically, medical containers such as I.V. bags are connected to a patient through a series of connected tubing that have drip chambers, Y-type injection sites, venous catheters and the like between the bag and the patient. Many of these components include rigid housings manufactured from polymers such as polycarbonates, acrylics, ABS and copolyesters. The housings have sleeves in which the tubing is inserted in a telescoping fashion to attach the tube to the housing. Therefore, it is necessary for the medical tubing to be connected to the rigid housing to form a fluid tight seal with the housings.
PVC tubing is typically secured within such housings using solvent bonding techniques. Solvent bonding requires exposing the end of the tubing to be inserted into the housing to a solvent such as cyclohexanone or methyl ethyl ketone. The solvent effectively softens or "melts" the PVC so when the tubing is inserted into the housing, a bond is formed. It is desirable that the outer tubing diameter be approximately the same dimension or slightly larger than the inner diameter of the housing to form an interference fit, as close tolerances in these dimensions assists in forming a secure bond.
Solvent bonding techniques, however, are ineffective on certain polyolefins including polyethylene. Problems have also been encountered in using adhesive bonding techniques.
One attempt at overcoming this problem was to use a two step process of applying a primer material to the surface to be bonded followed by an adhesive. Cyanoacrylate adhesives have worked with some success using this technique with a primer. However, the two step process adds an additional step to a manufacturing process which could slow down the production line and increase the labor costs. Further, primers increase the cost of the process. Third, because primers typically contain large quantities of volatile chemicals such as organic solvents, and might lead to toxicity, safety and environmental problems. Fourth, primers may limit manufacturing options as they have a limited on-part life time, i.e., the primers will lose their activities within hours after exposure to an ambient environment.
The present invention solves these and other problems.